The function of a sensory circuit depends on its cellular components, and changes in the state of these cells can lead to circuit dysfunction and disease. Olfaction is a primary sensory modality in multiple species, and in humans the sense of smell is one of the first sensory systems to become disrupted in neurodegenerative diseases. Despite the critical importance of olfaction, a full census of cell types in this system has not been completed. I propose to identify cell types in the mouse main olfactory bulb, the first site of information integration and processing in the main olfactory system. I will identify olfactory bulb cell types through the integration of transcriptomic (single cell RNA-sequencing) and epigenomic (single nucleus methylome- and single nucleus ATAC-sequencing) data generated by members of the BRAIN Initiative Cell Census Network (BICCN), a coalition of laboratories using advances in single-cell technology to map all of the cell types within select rodent and primate brains. Transcriptomic data provides a snapshot of a cell?s current state while epigenomic data provides information on currently active gene regulatory elements and the developmental history of a cell. Through the integration of these different modalities, a comprehensive census of cell types in the olfactory bulb will be generated (Aim 1). I will use the epigenomic profiling of these cells to identity gene regulatory elements in different cell types, including adult-born interneurons. This will allow for the identification of transcription factors that drive the maturation and survival of cells in an important sensory circuit (Aim 2). The proposed fellowship training will provide training in bioinformatics and statistical analysis from experts in the epigenome and transcriptome in UC San Diego and the BICCN.